Physical Characteristics, Release Properties, and Antioxidant and Antimicrobial Activities of Whey Protein Isolate Films Incorporated with Thyme (Thymus vulgaris L.) Extract-Loaded Nanoliposomes

The aim of the current research was to fabricate, characterize, and compare physical, mechanical, antimicrobial, antioxidant, and release properties of whey protein isolate (WPI)-based films containing free or nanoencapsulated thyme (Thymus vulgaris) extract (TE) at concentrations of 0, 5, 10, and 15% w/w of WPI. Nanoliposomes with an average size of 350 nm were prepared using thin-film hydration and sonication method. The data obtained from FTIR reflected the occurrence of some new interactions between WPI and nanoliposomes. XRD results approved the negative effect of free TE on the crystallinity of WPI. Besides, SEM images showed that free TE caused the cracks and holes in the WPI matrix to increase. However, the encapsulated TE did not show these negative effects. The nanoliposome incorporation improved the mechanical stiffness, leading to a decrease in the water vapor permeability (WVP). The possible antimicrobial activity of the films containing TE-loaded nanoliposomes against Staphylococcus aureus and Escherichia coli was decreased in comparison to the free TE-incorporated films, probably due to the inhibition effect of the encapsulation preventing the release of TE from the matrix. In addition, the antioxidant potential of the films containing TE-loaded nanoliposomes was lower than that of free TE-incorporated films. Release studies indicated that the migration of TE in ethanol 95% simulant decreased significantly by the nanoencapsulation of TE. However, the release rate increased by an increase in temperature in both types of active films. Therefore, this work showed that there is a potential for the production of antioxidant and antimicrobial controlled-release nanoactive WPI-TE films for use in food packaging and medical fields.